1. Field of the Invention
The present invention relates generally to a slide fastener, and more particularly to a slide fastener stringer comprising coupling elements each having a coupling portion composed of a pair of integral superposed head and support portions.
2. Prior Art
As shown in FIGS. 1 and 2, a known slide fastener comprises a pair of stringers each having a row of discrete molded coupling elements E mounted on and along a longitudinal edge of a stringer tape T. Each coupling element E has a coupling end portion projecting beyond the tape's longitudinal edge and composed of a pair of superposed head and support portions H, S disposed one on each side of the general plane P of the stringer tape T. The coupling element E is formed from a thermoplastic synthetic resin material such as nylon-66 by molding directly around the longitudinal edge of the tape T sandwiched between a pair of mold halves (not shown), so that the head and support portions H, S are separated by a mold parting line extending in the plane P of the tape T. Side surfaces A of the head and support portions H, S are bevelled at a suitable small angle to a normal to the tape T to allow the coupling element E to be easily removed from mold cavities in the mold halves during manufacture. The support portion S has recessed wings W disposed on opposide side of the head portion H, the wings W defining jointly with the head portions of a pair of adjacent coupling elements a pair of clearances or gaps G to allow the opposed rows of the coupling elements E to be smoothly coupled together.
When lateral pulling forces F are applied to the coupled stringers as shown in FIG. 1, the interdigitating head portions H are brought into abutting engagement together at the lower edge B of confronting bevelled side surfaces A, A thereof. The molded coupling elements are likely to be deformed at such load-bearing edges of the coupling end portions due to stresses concentrated therein. The coupled stringers having such deformed coupling elements are susceptible to accidental separation under severe lateral pulling forces applied thereto or a severe thrust applied perpendicularly to the plane P of the tape T. Since the gaps G extend near the general plane P of the tapes T, i.e. a plane of action of the lateral pulling forces F, the interdigitating coupling elements E, E are liable to be displaced away from each other in a direction perpendicular to the tape, as shown in FIG. 3.